We are studying the altered growth regulation of cancer cells, emphasizing tumor virology, cell differentiation, and cell surface immunology and biochemistry. We will characterize the genome structure, transforming proteins and regulation of expression of a variety of tumor viruses. We will attempt to define the functions of various transforming proteins and their relationship to cell growth control. We will characterize in detail the regulation of viral and cellular mRNA's using recombinant DNA techniques and nucleotide sequence analysis. We will use monoclonal antibodies and other markers to define the steps in differentiation of mammary hematopoietic and other cell types.